The present invention pertains to a device for applying free-flowing material to a movable substrate in particular for intermittent application of liquid adhesive, with at least one supply channel for supplying flowing material, at least one nozzle unit with at least one output channel, connected to the supply channel and ending in an output orifice for delivering material, and with a valve mechanism for interrupting the flow of material, having a movable valve body and a valve seat, where the valve body and the valve seat interact in such a way that the flow of material is interrupted by movement of the valve body to a closed position and is released by movement to an open position.
In industry a device of this type is used, for example, in order to coat the surfaces of film-type substrates with liquid adhesive, such as hot-melt glue. Often so-called intermittent application is used, meaning that intervals in which the valve body is in the open position and material is applied to the substrate alternate with intervals in which the valve body is in the closed position, so that the application of material is interrupted. Where application is intermittent, often very short intervals are used, in order to be able to realize application zones at very close intervals to each other. In some uses the flow of material needs to be interrupted up to 1000 times per minute.
The requirement for the pattern which takes shape on the substrate is that a zone where material is applied to the substrate must have sharply defined boundaries. In the case of application to an area with the help of a known slotted nozzle arrangement it is especially desired that the lateral margins--in the direction of movement of the substrate relative to the application device--, but also the leading and trailing boundaries of a zone where material is applied, be sharply delimited. Prerequisite for such sharp delimitation of the leading and trailing boundaries is that the body of the valve be moved quickly into its closed position, so that the flow of material from the output orifice is interrupted uniformly quickly. When the valve is opened, in order to achieve a sharp definition line at the leading boundary of an application zone it is necessary for the valve to open quickly.
In the current state of technology a so-called needle valve is used; as its valve body it has a needle with a needle point which can be brought into contact with a valve seat which matches the shape of the needle point. To close the valve, the needle is moved--by an electrical-pneumatic mechanism--in the direction of the valve seat and comes into contact with the latter, so that the flow section of the supply channel is closed and the flow of material is thereby interrupted. During the closing movement of the needle point the latter is moved in the direction of flow, toward the substrate. During the closing movement of the needle point adhesive is forced downstream by the needle point in the direction of the output orifices. This has the effect that until the needle point comes into contact with the valve seat, material is forced in the direction of the output orifice. As a consequence, the application of material to the substrate is not interrupted as abruptly as would be necessary to produce a sharp line of demarcation in the end area of an application zone. "Afterdripping" from the output orifice when the valve is closed cannot be prevented.